1. FIELD OF THE INVENTION
This invention relates to the production of hexamethyleneimine by the catalytic hydrogenation of .epsilon.-caprolactam.
2. DESCRIPTION OF THE PRIOR ART
Hexamethyleneimine, an intermediate used in the production of herbicides and insecticides, has heretofore been commercially produced as a by-product in the production of hexamethylenediamine, a nylon-6,6 monomer, in which either adiponitrile is reduced or 1,6-hexanediol is aminated. Such processes are indirect, low yield routes to hexamethyleneimine ("HMI"). It has previously been suggested to prepare HMI directly by the vapor phase reaction of oxepane and ammonia (U.S. Pat. No. 3,635,952 issued to Tyssee et al. in 1972) and by the vapor phase reaction of tetrahydropyran-2-methanol, hydrogen and ammonia (U.S. Pat. No. 3,635,951 issued to Tyssee et al. in 1972). However, such processes require the utilization of expensive and uncommon starting materials. It has also been heretofore suggested in U.S. Pat. No. 2,181,140 issued to Lazier et al. in 1939 to prepare HMI together with hexamethylenediamine by the catalytic hydrogenation of .epsilon.-caprolactam using Group VIII, Group IB or Group IIB metals as catalysts. The Lazier et al. patent is primarily directed to the production of hexamethylenediamine and although in the penultimate paragraph thereof it is broadly stated that by altering the hydrogenation conditions HMI can be obtained, such conditions are not disclosed.